1. Field of the Invention
This invention relates to a 6-group 7-lens modified Gauss type phototaking lens which has an angle of view 46.degree. and a brightness amounting to about F1.4 and which is compact and has a great quantity of marginal light.
2. Description of the Prior Art
Generally, Guass type lenses have a relatively flat image plane and permit their back focal length to be selected to about 0.7f or longer and therefore, are often used as a great aperture ratio lens such as, for example, a single lens reflex which requires a relatively long back focal length, but most of them have about 10%-23% of aperture efficiency at an incidence angle of 23.degree. with respect to off-axis light rays and have a disadvantage that decrease in quantity of marginal light is salient.
To increase aperture efficiency, that is, to reduce the vignetting of lens, a method of increasing the diameter of the foremost lens which limits the off-axis light beam and the diameter of the rearmost lens and a method of reducing the full length of the lens are conceivable, but increasing the lens diameter prevents the lens from becoming compact and increased diameter of the foremost lens leads to bulkiness of the attachment connected immediately before the foremost lens and increased diameter of the rearmost lens leads to bulkiness of the device around the lens such as increased diameter of the lens mounting surface with respect to the camera body provided near the rearmost lens, and these are not preferable. Also, reducing the full length of the lens is effective as the means for increasing the quantity of marginal light without increasing the diameter of the lens while, on the other hand, it leads to a sharp increase in coma flare and therefore, reducing the full length of the lens limitlessly is not desirable, and where the aperture efficiency of light ray of an incidence angle of 23.degree. is about 25% even in the heretofore known compact type lens, the disadvantage that coma flare of light rays in the vicinity of an incidence angle of 6.degree. becomes particularly excessive has been unavoidable.